Typical commercial off the shelf (COTS) wireless devices do not meet the electromagnetic interference/radio frequency interference, environmental and certification requirements of most aerospace applications. These COTS wireless products require significant human intervention to configure them for every operational scenario. Widely deployed wireless technologies, including Institute of Electrical and Electronics Engineers (IEEE) 802.11 and IEEE 802.15.4, use carrier sensing multiple access with collision avoidance (CSMA/CA) techniques for channel access. Although CSMA/CA techniques are well-known to be suitable for variable and unpredictable traffics, they suffer from severe control overhead when the traffic is predictable or regular. In addition, current 802.11 and 802.15.4 have no Quality of Service (QoS) guarantees due to the probabilistic nature of CSMA/CA and no prioritization among wireless nodes. IEEE Standard 802.11e includes a QoS extension to 802.11. In 802.11e, the traffic priority is differentiated by Traffic Categories (TCs) and the QoS is managed by two operation modes: (1) enhanced distributed coordination function (EDCF); and (2) hybrid coordination function (HCF). Even though 802.11e provides better medium access probability to higher priority traffic at the price of high control overhead, it still does not provide any QoS guarantees to the applications.
In most aerospace applications, the data traffic, such as video, audio, sensor/actuator data, and real-time control signal, are predictable or regular. Furthermore, some data traffics, such as control signals and sensor/actuator data, usually demand some type of guaranteed QoS.
It is difficult to optimize the user of resources to maximize network throughput and to minimize network energy consumption. As the network size increases, the computation of the optimal solution becomes prohibitively complex. Some wireless Time Division Multiple Access (TDMA) technologies, e.g., Bluetooth and low energy adaptive clustering hierarchy (LEACH), start with generic applications of random data traffic and optimize the resources for either throughput or energy conservation or both. In order to be computable, Bluetooth and LEACH make assumptions, which impose limitations on their applications.
For instance, Bluetooth is limited to eight active nodes in a cluster. LEACH is an energy efficient protocol for wireless sensor network, which is a mixture of CSMA, TDMA and code division multiple access (CDMA).
In LEACH, the advertisement phase and cluster set-up phase use CSMA, the schedule creation and data transmission use TDMA. The nodes inside one cluster communicate to each other using a CDMA code that is different from the CDMA code of nearby clusters in order to avoid signal corruption from the nearby clusters. In addition to its algorithmic complexity, LEACH assumes that each node knows a priori the optimum average number of clusters for the network. This assumption makes LEACH unable to adapt to dynamically changing network topology.
The data rate adaptation for TDMA technologies is done based on the detected packet errors. The transmitter switches to a higher transmission rate after a certain number of successful transmissions and changes to a lower rate after a fixed number of consecutive failures. This packet error method wastes resources since there are failures from periodically attempting higher data rate.